New low band gap thieno[3,4-b]thiophene-based polymers with deep HOMO levels for organic solar cells
作者:Salem Wakim、Salima Alem、Zhao Li、Yanguang Zhang、Shing-Chi Tse、Jianping Lu、Jianfu Ding、Ye Tao
DOI:10.1039/c1jm11229e
日期:——
Two new soluble alternating alkyl-substituted benzo[1,2-b:4,5-b′]dithiophene and ketone-substituted thieno[3,4-b]thiophene copolymers were synthesized and characterized. We found that grafting 3-butyloctyl side chains to the benzo[1,2-b:4,5-b′]dithiophene unit at C4 and C8 afforded the resulting polymer (P1) a high hole mobility (∼10−2 cm2Vs−1) and a low-lying HOMO energy level (5.22 eV). Preliminary experiments in bulk heterojunction solar cells using P1 as the electron donor demonstrated a high power conversion efficiency of 4.8% even with PC61BM as the electron acceptor. The introduction of an electron-withdrawing fluorine atom into the thieno[3,4-b]thiophene unit at the C3 position (P2) lowers the HOMO energy level and consequently improves the open circuit voltage from 0.78 to 0.86 V. These values are about 0.1 V higher than those reported for their analogues based on alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene. This work demonstrates that the replacement of the alkoxy chains on the benzo[1,2-b:4,5-b′]dithiophene unit with less electron-donating alkyl chains is able to lower the HOMO energy levels of this class of polymers without increasing their band gap energy.
合成并表征了两种新的可溶性交替烷基取代苯并[1,2-b:4,5-b′]二噻吩和酮取代噻吩并[3,4-b]噻吩共聚物。我们发现,将 3-丁辛基侧链接枝到苯并[1,2-b:4,5-b′]二噻吩单元的 C4 和 C8 处,可使聚合物(P1)具有较高的空穴迁移率(∼10-2 cm2Vs-1)和较低的 HOMO 能级(5.22 eV)。以 P1 为电子供体的体异质结太阳能电池的初步实验表明,即使以 PC61BM 为电子受体,其功率转换效率也高达 4.8%。在噻吩并[3,4-b]噻吩单元的 C3 位置(P2)引入一个电子吸收氟原子降低了 HOMO 能级,从而将开路电压从 0.78 V 提高到 0.86 V。这项工作表明,用较少电子捐赠的烷基链取代苯并[1,2-b:4,5-b′]二噻吩单元上的烷氧基链,能够降低这类聚合物的 HOMO 能级,而不增加其带隙能。